Dynamic Rearrangement and Directional Migration of Tubular Vacuoles are Required for the Asymmetric Division of the Arabidopsis Zygote

2021 ◽  
Author(s):  
Hikari Matsumoto ◽  
Yusuke Kimata ◽  
Takumi Higaki ◽  
Tetsuya Higashiyama ◽  
Minako Ueda
Keyword(s):  
Asymmetric Cell Division ◽  
Initial Step ◽  
Vacuolar Membrane ◽  
Axis Formation ◽  
Basal Region ◽  
Core Component ◽  
Directional Migration ◽  
Formation Pathway ◽  
Directional Movement ◽  
Sites Of Action

Abstract In most flowering plants, asymmetric cell division of zygotes is the initial step to establish the apical–basal axis. In the Arabidopsis zygote, vacuolar accumulation at the basal cell end is crucial to ensure zygotic division asymmetry. Despite the importance, it was unclear whether this polar vacuolar distribution is achieved by predominant biogenesis at the basal region or by directional movement after biogenesis. Here, we found that apical and basal vacuolar contents are dynamically exchanged via tubular vacuolar network and the vacuoles gradually migrate towards the basal end. The mutant of a vacuolar membrane protein, SHOOT GRAVITROPISM2 (SGR2), failed to form tubular vacuoles, and the mutant of a putative vacuolar fusion factor, VESICLE TRANSPORT THROUGH INTERACTION WITH T-SNARES11 (VTI11), could not flexibly rearrange the vacuolar network. Both mutants failed to exchange the apical and basal vacuolar contents and to polarly migrate the vacuoles, resulting in more symmetric division of zygotes. Additionally, we observed that in contrast to sgr2, the zygotic defects of vti11 were rescued by the pharmacological depletion of phosphatidylinositol 3-phosphate (PI3P), a distinct phospholipid in the vacuolar membrane. Thus, SGR2 and VTI11 have individual sites of action in the zygotic vacuolar membrane processes. Further, a mutant of YODA (YDA) MAPKK kinase, a core component of the embryonic axis formation pathway, generated proper vacuolar network; however, it failed to migrate the vacuoles towards the basal region, which suggests impaired directional cues. Overall, we conclude that SGR2- and VTI11-dependent vacuolar exchange and YDA-mediated directional migration are necessary to achieve polar vacuolar distribution in the zygote.

scholarly journals Polar vacuolar distribution is essential for accurate asymmetric division ofArabidopsiszygotes

2019 ◽  
Vol 116 (6) ◽  
pp. 2338-2343 ◽  
Author(s):  
Yusuke Kimata ◽  
Takehide Kato ◽  
Takumi Higaki ◽  
Daisuke Kurihara ◽  
Tomomi Yamada ◽  
...  
Keyword(s):  
Actin Filaments ◽  
Live Cell Imaging ◽  
Asymmetric Cell Division ◽  
Imaging System ◽  
Initial Step ◽  
Asymmetric Distribution ◽  
Basal Region ◽  
Polar Localization ◽  
Polar Distribution

In most flowering plants, the asymmetric cell division of the zygote is the initial step in establishing the apical–basal axis of the mature plant. The zygote is polarized, possessing the nucleus at the apical tip and large vacuoles at the basal end. Despite their known polar localization, whether the positioning of the vacuoles and the nucleus is coordinated and what the role of the vacuole is in the asymmetric zygotic division remain elusive. In the present study, we utilized a live-cell imaging system to visualize the dynamics of vacuoles during the entire process of zygote polarization inArabidopsis. Image analysis revealed that the vacuoles formed tubular strands around the apically migrating nucleus. They gradually accumulated at the basal region and filled the space, resulting in asymmetric distribution in the mature zygote. To assess the role of vacuoles in the zygote, we screened various vacuole mutants and identified thatshoot gravitropism2(sgr2), in which the vacuolar structural change was impaired, failed to form tubular vacuoles and to polarly distribute the vacuole. Insgr2, large vacuoles occupied the apical tip and thus nuclear migration was blocked, resulting in a more symmetric zygotic division. We further observed that tubular vacuole formation and asymmetric vacuolar distribution both depended on the longitudinal array of actin filaments. Overall, our results show that vacuolar dynamics is crucial not only for the polar distribution along actin filaments but also for adequate nuclear positioning, and consequently zygote-division asymmetry.

scholarly journals Mec1/Tel1-independent role of protein phosphatase 4 in Hop1 assembly to promote meiotic chromosome axis formation in budding yeast

2021 ◽  
Author(s):  
Miki Shinohara
Keyword(s):  
Protein Phosphatase ◽  
Budding Yeast ◽  
Meiotic Chromosome ◽  
Integrated Control ◽  
Initial Step ◽  
Axis Formation ◽  
Recombination Reaction ◽  
Chromosomal Structure ◽  
Aaa Atpase ◽  
Chromosome Axis

Dynamic changes in chromosomal structure that occur during meiotic prophase play an important role in the progression of meiosis. Among them, meiosis-specific chromosomal axis-loop structures are important as a scaffold for integrated control between the meiotic recombination reaction and the associated checkpoint system to ensure accurate chromosome segregation. However, the molecular mechanism of the initial step of chromosome axis-loop construction is not well understood. Here, we showed that, in budding yeast, a Tel1/Mec1-related protein phosphatase 4 (PP4) is required to promote the assembly of a chromosomal axis components Hop1 and Red1 onto meiotic chromatin via interaction with Hop1. PP4 did not affect Rec8 assembly. Notably, unlike the previously known function of PP4, this novel function was independent of Tel1/Mec1 kinase functions. The defect in Hop1/Red1 assembly in the absence of PP4 function was not suppressed by Pch2 dysfunction. Since Pch2 is a conserved AAA+ ATPase and facilitates eviction of Hop1 protein from the chromosome axis, suggesting that PP4 is required for the initial step of chromatin loading of Hop1 rather than stabilizing Hop1 on the chromosome axis. These results indicate phosphorylation/dephosphorylation-mediated regulation of Hop1 recruitment onto chromatin during chromosome axis construction before meiotic double-strand break formation.

scholarly journals Biogenesis of Tom40, Core Component of the Tom Complex of Mitochondria

1999 ◽  
Vol 146 (2) ◽  
pp. 321-332 ◽  
Author(s):  
Doron Rapaport ◽  
Walter Neupert
Keyword(s):  
Outer Membrane ◽  
Initial Step ◽  
Terminal Segment ◽  
Mitochondrial Outer Membrane ◽  
Core Component ◽  
Core Element ◽  
The Core ◽  
Tom Complex ◽  
Partially Folded Conformation ◽  
Import Receptor

Tom40 is an essential component of the preprotein translocase of the mitochondrial outer membrane (TOM complex) in which it constitutes the core element of the protein conducting pore. We have investigated the biogenesis of Tom40. Tom40 is inserted into the outer membrane by the TOM complex. Initially, Tom40 is bound as a monomer at the mitochondrial surface. The import receptor Tom20 is involved in this initial step; it stimulates both binding and efficient insertion of the Tom40 precursor. This step is followed by the formation of a further intermediate at which the Tom40 precursor is partially inserted into the outer membrane. Finally, Tom40 is integrated into preexisting TOM complexes. Efficient import appears to require the Tom40 precursor to be in a partially folded conformation. Neither the NH2 nor the COOH termini are necessary to target Tom40 to the outer membrane. However, the NH2-terminal segment is required for Tom40 to become assembled into the TOM complex. A model for the biogenesis of Tom40 is presented.

scholarly journals Rac1 and Aurora A regulate MCAK to polarize microtubule growth in migrating endothelial cells

2014 ◽  
Vol 206 (1) ◽  
pp. 97-112 ◽  
Author(s):  
Alexander Braun ◽  
Kyvan Dang ◽  
Felinah Buslig ◽  
Michelle A. Baird ◽  
Michael W. Davidson ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Growth Dynamics ◽  
Aurora A Kinase ◽  
Aurora A ◽  
Directional Migration ◽  
Directional Movement ◽  
Associated Proteins ◽  
Guanosine Triphosphatase ◽  
And Migration ◽  
Computational Image Analysis

Endothelial cells (ECs) migrate directionally during angiogenesis and wound healing by polarizing to extracellular cues to guide directional movement. EC polarization is controlled by microtubule (MT) growth dynamics, which are regulated by MT-associated proteins (MAPs) that alter MT stability. Mitotic centromere-associated kinesin (MCAK) is a MAP that promotes MT disassembly within the mitotic spindle, yet its function in regulating MT dynamics to promote EC polarity and migration has not been investigated. We used high-resolution fluorescence microscopy coupled with computational image analysis to elucidate the role of MCAK in regulating MT growth dynamics, morphology, and directional migration of ECs. Our results show that MCAK-mediated depolymerization of MTs is specifically targeted to the trailing edge of polarized wound-edge ECs. Regulation of MCAK function is dependent on Aurora A kinase, which is regionally enhanced by signaling from the small guanosine triphosphatase, Rac1. Thus, a Rac1–Aurora A–MCAK signaling pathway mediates EC polarization and directional migration by promoting regional differences in MT dynamics in the leading and trailing cell edges.

scholarly journals Pharmacological glycerol-3-phosphate acyltransferase inhibition decreases food intake and adiposity and increases insulin sensitivity in diet-induced obesity

2011 ◽  
Vol 301 (1) ◽  
pp. R116-R130 ◽  
Author(s):  
Francis P. Kuhajda ◽  
Susan Aja ◽  
Yajun Tu ◽  
Wan Fang Han ◽  
Susan M. Medghalchi ◽  
...  
Keyword(s):  
Gene Expression ◽  
Weight Loss ◽  
Insulin Sensitivity ◽  
Energy Intake ◽  
Respiratory Exchange Ratio ◽  
Initial Step ◽  
Partial Protection ◽  
Diet Induced Obesity ◽  
Brown Adipose ◽  
Sites Of Action

Storage of excess calories as triglycerides is central to obesity and its associated disorders. Glycerol-3-phosphate acyltransferases (GPATs) catalyze the initial step in acylglyceride syntheses, including triglyceride synthesis. We utilized a novel small-molecule GPAT inhibitor, FSG67, to investigate metabolic consequences of systemic pharmacological GPAT inhibition in lean and diet-induced obese (DIO) mice. FSG67 administered intraperitoneally decreased body weight and energy intake, without producing conditioned taste aversion. Daily FSG67 (5 mg/kg, 15.3 μmol/kg) produced gradual 12% weight loss in DIO mice beyond that due to transient 9- to 10-day hypophagia (6% weight loss in pair-fed controls). Continued FSG67 maintained the weight loss despite return to baseline energy intake. Weight was lost specifically from fat mass. Indirect calorimetry showed partial protection by FSG67 against decreased rates of oxygen consumption seen with hypophagia. Despite low respiratory exchange ratio due to a high-fat diet, FSG67-treated mice showed further decreased respiratory exchange ratio, beyond pair-fed controls, indicating enhanced fat oxidation. Chronic FSG67 increased glucose tolerance and insulin sensitivity in DIO mice. Chronic FSG67 decreased gene expression for lipogenic enzymes in white adipose tissue and liver and decreased lipid accumulation in white adipose, brown adipose, and liver tissues without signs of damage. RT-PCR showed decreased gene expression for orexigenic hypothalamic neuropeptides AgRP or NPY after acute and chronic systemic FSG67. FSG67 given intracerebroventricularly (100 and 320 nmol icv) produced 24-h weight loss and feeding suppression, indicating contributions from direct central nervous system sites of action. Together, these data point to GPAT as a new potential therapeutic target for the management of obesity and its comorbidities.

scholarly journals Migration of the 3T3 Cell with a Lamellipodium on Various Stiffness Substrates—Tensegrity Model

2020 ◽  
Vol 10 (19) ◽  
pp. 6644
Author(s):  
Arkady Voloshin
Keyword(s):  
Elastic Strain ◽  
Strain Energy ◽  
Elastic Strain Energy ◽  
Substrate Stiffness ◽  
Mechanical Stimuli ◽  
Directional Migration ◽  
Directional Movement ◽  
A Cell ◽  
Tensegrity Model

Changes in mechanical stimuli and the physiological environment are sensed by the cell. Thesechanges influence the cell’s motility patterns. The cell’s directional migration is dependent on the substrate stiffness. To describe such behavior of a cell, a tensegrity model was used. Cells with an extended lamellipodium were modeled. The internal elastic strain energy of a cell attached to the substrates with different stiffnesses was evaluated. The obtained results show that on the stiffer substrate, the elastic strain energy of the cell adherent to this substrate decreases. Therefore, the substrate stiffness is one of the parameters that govern the cell’s directional movement.

Preparation of Electron Transparent Metal-Matrix Composites

1968 ◽  
Vol 26 ◽  
pp. 334-335 ◽  
Author(s):  
M. R. Pinnel ◽  
A. Lawley
Keyword(s):  
Stainless Steel ◽  
Load Transfer ◽  
Volume Fraction ◽  
Steel Wire ◽  
Initial Step ◽  
Interfacial Region ◽  
Matrix Composites ◽  
Specific Test ◽  
The Matrix ◽  
The One

Numerous phenomenological descriptions of the mechanical behavior of composite materials have been developed. There is now an urgent need to study and interpret deformation behavior, load transfer, and strain distribution, in terms of micromechanisms at the atomic level. One approach is to characterize dislocation substructure resulting from specific test conditions by the various techniques of transmission electron microscopy. The present paper describes a technique for the preparation of electron transparent composites of aluminum-stainless steel, such that examination of the matrix-fiber (wire), or interfacial region is possible. Dislocation substructures are currently under examination following tensile, compressive, and creep loading. The technique complements and extends the one other study in this area by Hancock.The composite examined was hot-pressed (argon atmosphere) 99.99% aluminum reinforced with 15% volume fraction stainless steel wire (0.006″ dia.).Foils were prepared so that the stainless steel wires run longitudinally in the plane of the specimen i.e. the electron beam is perpendicular to the axes of the wires. The initial step involves cutting slices ∼0.040″ in thickness on a diamond slitting wheel.

The Advantages of Cryotechniques: Application To Bioluminescent Cells

1990 ◽  
Vol 48 (1) ◽  
pp. 486-487
Author(s):  
Gisèle Nicolas ◽  
Jean-Marie Bassot ◽  
Marie-Thérèse Nicolas
Keyword(s):  
Endoplasmic Reticulum ◽  
Striated Muscle ◽  
Light Emission ◽  
Stable State ◽  
Freeze Substitution ◽  
Initial Step ◽  
Point Of Interest ◽  
Cell Components ◽  
Excellent Preservation ◽  
External Water

The use of fast-freeze fixation (FFF) followed by freeze-substitution (FS) brings substantial advantages which are due to the extreme rapidity of this fixation compared to the conventional one. The initial step, FFF, physically immobilizes most molecules and therefore arrests the biological reactions in a matter of milliseconds. The second step, FS, slowly removes the water content still in solid state and, at the same time, chemically fixes the other cell components in absence of external water. This procedure results in an excellent preservation of the ultrastructure, avoids osmotic artifacts,maintains in situ most soluble substances and keeps up a number of cell activities including antigenicities. Another point of interest is that the rapidity of the initial immobilization enables the capture of unstable structures which, otherwise, would slip towards a more stable state. When combined with electrophysiology, this technique arrests the ultrastructural modifications at a well defined state, allowing a precise timing of the events.We studied the epithelium of the elytra of the scale-worm, Harmothoe lunulata which has excitable, conductible and bioluminescent properties. The intracellular sites of the light emission are paracrystals of endoplasmic reticulum (PER), named photosomes (Fig.1). They are able to flash only when they are coupled with plasma membrane infoldings by dyadic or triadic junctions (Fig.2) basically similar to those of the striated muscle fibers. We have studied them before, during and after stimulation. FFF-FS showed that these complexes are labile structures able to diffentiate and dedifferentiate within milliseconds. Moreover, a transient network of endoplasmic reticulum was captured which we have named intermediate endoplasmic reticulum (IER) surrounding the PER (Fig.1). Numerous gap junctions are found in the membranous infoldings of the junctional complexes (Fig.3). When cryofractured, they cleave unusually (Fig.4-5). It is tempting to suggest that they play an important role in the conduction of the excitation.

Centrosome Aurora A gradient ensures single polarity axis in C. elegans embryos

2020 ◽  
Vol 48 (3) ◽  
pp. 1243-1253 ◽  
Author(s):  
Sukriti Kapoor ◽  
Sachin Kotak
Keyword(s):  
Symmetry Breaking ◽  
Cell Fate ◽  
Cell Cortex ◽  
Axis Formation ◽  
Aurora A Kinase ◽  
Aurora A ◽  
C Elegans ◽  
Cell Embryo ◽  
Polarity Establishment

Cellular asymmetries are vital for generating cell fate diversity during development and in stem cells. In the newly fertilized Caenorhabditis elegans embryo, centrosomes are responsible for polarity establishment, i.e. anterior–posterior body axis formation. The signal for polarity originates from the centrosomes and is transmitted to the cell cortex, where it disassembles the actomyosin network. This event leads to symmetry breaking and the establishment of distinct domains of evolutionarily conserved PAR proteins. However, the identity of an essential component that localizes to the centrosomes and promotes symmetry breaking was unknown. Recent work has uncovered that the loss of Aurora A kinase (AIR-1 in C. elegans and hereafter referred to as Aurora A) in the one-cell embryo disrupts stereotypical actomyosin-based cortical flows that occur at the time of polarity establishment. This misregulation of actomyosin flow dynamics results in the occurrence of two polarity axes. Notably, the role of Aurora A in ensuring a single polarity axis is independent of its well-established function in centrosome maturation. The mechanism by which Aurora A directs symmetry breaking is likely through direct regulation of Rho-dependent contractility. In this mini-review, we will discuss the unconventional role of Aurora A kinase in polarity establishment in C. elegans embryos and propose a refined model of centrosome-dependent symmetry breaking.

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